Freeze drying method and apparatus



Nov. 28, 1967 w. NERGE ET AL FREEZE DRYING METHOD AND APPARATUS 1 .9 m asss v e w w MN MW 5 .n H T W I ww rmkn uswuku k "m A 4 m 5 WOW vmfifiwfiwdu s MV 1 am iv .n mm by Him w LN Mi k H NOV. 28, 1967 w, MERGE ET AL FREEZE DRYING METHOD AND APPARATUS 2 SheetsSheet 2 United States Patent Claims. oi. 53-412 This invention relates to a method and apparatus for the freeze drying of moisture containing products and more particularly to a method and apparatus for the freeze drying of instant food products.

Freeze drying is a well-known process in which a material to be dried is first frozen and then placed inside an evacuable chamber. Water vapor removal apparatus, such as, for example, a deep-cooled ice condenser, then absorbs sublimating water vapor produced by heating of the frozen material. A predetermined low pressure is continuously maintained within the vacuum chamber during the drying process by means of conventional vacuum pumps communicating with the chamber.

One of the more costly functions in the freeze drying process relates to the handling of the containers in which the products are dried. These containers of various shapes are filled with the product to be dried, frozen and then evacuated under the influence of heat in the drying chamber. The mass ratio of product containers to product is relatively large because the product can be dried and easily handled in only relatively small volumes in addition to the normal requirement that the product containers be relatively thick (for example, greater than 1 mm.) so as to exhibit good heat transfer characteristics. Therefore there is a large energy cost for first deep freezing the containers and then during the drying process beating them in stages up to 80 C. or higher. These costs are especially high in the large, continuous freeze drying installations which are currently coming into extensive use. Also the extensive handling of both the product and the product containers is expensive. The product must be prepared for freezing, placed into drying containers, loaded into a freeze dry installation before the process can begin. Then upon completion of the freeze drying process, the dried material must be removed from the drying containers and packed into different packages for distribution to commercial consumers. For many products, this final packaging is complicated by the requirement that the packaging be vacuum tight and accomplished in an inert atmosphere such as, for example, of nitrogen. Upon completion of one drying cycle, the drying containers, which have frequently been quite soiled by burned product, must be thoroughly Washed and dried before reuse.

The object of this invention, therefore, is to provide a more efiicient freeze drying installation which substantially reduces process costs associated with handling of the freeze dry product and product containers.

One feature of this invention is the provision of a freeze drying installation including an evacuable chamber which houses heating plates, a conveyor device adapted to transport product filled containers into heat exchange relationship with the heating plates, and vacuum sealing apparatus adapted to gas tightly seal the product filled containers upon completion of the freeze drying process.

Another feature of the invention is the provision of a freeze drying installation of the above featured type including a fluid valve mechanism for isolating the heating plates and sealing apparatus into individual evacuable chamber sections.

Another feature of this invention is the provisions of a freeze drying installation of the above featured types wherein the sealing apparatus is adapted to gas tightly seal a metallic cover on an open metallic product container.

Another feature of the invention is the provision of a freeze drying installation of the above featured types wherein the heating plates are adapted to directly support the product containers and the conveyor device is adapted to move the product containers along the surfaces of the heating plates.

Another feature of the invention is the provision of a product container for use in freeze drying installations of the above featured types which product container is constructed of a metal less than 1 mm. thick, comprises a plurality of separated laterally arranged sections and contains perforations adapted for engagement with a toothed driving gear.

These and other objects and features of the present invention will be apparent upon an examination of the following description taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic cross sectional view of the complete freeze drying installation according to the subject invention;

FIG. 2 is a schematic transverse sectional view of the freeze drier drying section shown in FIG. 1;

FIG. 3 is a schematic partial longitudinal section of the drying chamber of FIG. 2 showing more clearly the heater plates, product containers and driving gears;

FIG. 4 is a schematic transverse sectional view of another drying chamber and conveyor mechanism embodiment of the present invention; and

FIG. 5 is an enlarged partial perspective view of the product containers shown in FIG. 4.

Referring now to FIGS. 1-3, there is shown an evacuable freeze drying tunnel chamber 11 having a drying section 12 straddled by the inlet lock section 13 and the sealing section 14. Demountable inlet and outlet doors 1'15, 16 provide access into the inlet lock section 13 and sealing section 14 respectively. The hydraulic valves 17, 18 which are operable by conventional apparatus (not shown) to isolate the drying section 12 from the inlet lock section 13 and sealing section 14.

Positioned in each of the drying, inlet lock and sealing sections are a plurality of horizontally arranged heating plates 21 which support the product containers 22. Each of the product containers comprises a flat metallic sheet into which a plurality of laterally adjacent independent depressions 23 have been stamped leaving fiat ridges 24 surrounding each depression. Suitable power means (not shown) drive the shafts 25 and attached toothed gears 26 which engage perforations 27 to transport each product container 22 along the surfaces of the heating plates 21.

Located in the sealing section 14 beyond the heating plates 21 is the lift surface 31 which is powered by a suitable lift mechanism (not shown). Above the lift surface 31 is the stamping press 32 beside which are stored a supply of metallic foil cover 33.

In the operation of the freeze drying installation 11, the depressions 23 are filled with a product to be dried and the filled product containers 22 are placed into inlet lock 13 through the inlet door 15. At this time, the valve 17 is closed to maintain vacuum (of about 10- mm. Hg) in the drying section 12 and the product to be dried is deep frozen if freezing has not been accomplished previously.

After the inlet lock section 13 has been adequately evacuated by suitable vacuum pumps (not shown), the valve 17 is opened and the product containers 22 are conveyed along the heater plate 21 surfaces slowly through the drying and sealing sections 12, 14 by the driving gears 26. Under the influence of the heat provided by heating plates 21, the freeze drying process will continue in the drying and sealing sections with valve 17 again closed. When the drying is completed of the product contained in those product containers within the sealing chamber 14, individual product containers are sequentially conveyed onto the lift surface 31 which has been laterally aligned therewith. Each such container is then lifted into contact with a metallic foil cover 33 which has been positioned above the lift surface 31 by suitable automatic equipment (not shown). Further lifting produces contact with the heated sealing press 32 which gas tightly seals the cover 33 to the product container 22. If desired, the underside of the foil covers may be coated with a suitable sealing material such as, for example, a polyvinyl resin. After being sealed, the product containers 22 are stacked in outlet lock 34 on rollers 35 adjacent the outlet door 16 ready for removal therethrough.

The entire sealing operation is performed under vacuum so that the product in the product container is vacuum sealed. In some instances a superior product results from packaging in an inert atmosphere. For this purpose the above sealing operation can be performed after closing the valve 18 to isolate drying section 12 and flooding the sealing section 14 with an inert gas, such as, for example, nitrogen.

The preferred product containers 22 constructed of metallic foil having a thickness less than 1 mm. are particularly suited for this application. They provide relatively good heat transfer between the heating plates 21 and the product to be dried in addition to exhibiting a relatively small mass. The small mass is important from a handling standpoint as well as for reducing the energy needed to accomplish the sequential deep freezing and heating requirements of the freeze drying process. Also, since the containers serve as both processing containers and final packaging many of the normally required product and container handling steps are eliminated.

Referring now to FIG. 4, there is shown another product container and conveyor embodiment of the invention. Shown in the drying section 12 are vertically arranged heating plates 41 separated by a free space of a few centimeters. The heating plates 41 are supported from the bottom of the drying section by a heating system 42. Fixed to the upper portion of the drying section 12 is a guide'rail 43 movably supporting a rack assembly 44. The rack assembly is moved by the gear chain 45 mounted on the insulated shaft 47 which is driven by a motor 48. Suspended from the rack assembly between adjacent heating plates 41 are the product containers 51.

As shown in FIG. 5, the product containers 51 are formed by individual pans 52 whose open sides are welded to a metallic foil sheet 53. The top sides of the pans 52 are peeled back to form flaps 54. Along the top surface of the foil sheet 53 are openings 55 adapted for attachment to the rack assembly 44.

The use of the embodiment of FIGS. 4 and is similar to that for the embodiment of FIGS. 1-3. The pans 52 are filled with a product which is then subjected to the freeze drying process within the tunnel 11 as described above. Upon completion of the freeze drying process, the pans 52 are gas tightly sealed under either vacuum or an inert atmosphere by sealing closed the pan flaps 54.

After completion of the freeze drying and sealing operations, the gas tightly sealed product is removed from the vacuum tunnel 11 through the outlet door 16. If de- I sired, the individual pans 52 or the individual depression sections 23 can then be separated into individual units for eventual distribution to commercial consumers.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. Apparatus for freeze-drying moisture-containing materials placed in heat-conductive traylike product containers, wherein the containers include bowl-like depressions and surrounding ridges, said container ridges being provided with means engageable by a conveyor means; said apparatus comprising:

chamber means adapted for evacuation to below atmospheric pressure; heating means positioned Within said chamber means, for heating the product containers and the product to be freeze dried; sealing means positioned within said chamber means for vacuum-tightly sealing the product containers; conveyor means positioned within said chamber for engaging the ridges of product containers to transport the containers in proximity to said heating means and to said sealing means.

2. Apparatus as set forth in claim 1:

wherein said heating means includes a flat supporting surface extending along said chamber, for supporting traylike product containers and for heating said containers by conduction; and wherein said conveyor means is disposed adjacent to said heating means for engaging said product containers to move said containers along said supporting surface in heat transfer relation.

3. Apparatus as set forth in claim 2:

wherein said conveyor means includes toothed wheels positioned in spaced relation to the flat supporting surface of said heating means, for engaging spaced recesses in the ridges of product containers for the purposse of moving said containers along said supporting surface.

4. Apparatus as set forth in claim 1:

wherein said sealing means includes means for positioning covers over product containers, and for sealing the covers to the containers.

5. Apparatus as set forth in claim 1:

wherein said heating means defines a plurality of fl'at supporting surfaces lying in parallel planes, for supporting traylike product containers and for heating said containers by conduction; and wherein said conveyor means comprises means for transporting product containers along each of said supporting surfaces in heat transfer relation.

References Cited UNITED STATES PATENTS 2,508,107 5/1950 Flosdor-f et al 99-199 2,517,569 8/1950 Huzenlaub 99--155 3,088,222 5/1963 Mace et al. 34-5 X 3,192,645 7/1965 Oetjen et al 34--92 3,233,333 2/1966 Oppenheimer. 3,234,661 2/1966 *Nerge 34-92 TRAVIS s. McGEI-IEE, Primary Examiner. 

1. APPARATUS FOR FREEZE-DRYING MOISTURE-CONTAINING MATERIALS PLACED IN HEAT-CONDUCTIVE TRAYLIKE PRODUCT CONTAINERS, WHEREIN THE CONTAINERS INCLUDE BOWL-LIKE DEPRESSIONS AND SURROUNDING RIDGES, SAID CONTAINER RIDGES BEING PROVIDED WITH MEANS ENGAGEABLE BY A CONVEYOR MEANS; SAID APPARATUS COMPRISING: CHAMBER MEANS ADAPTED FOR EVACUATION TO BELOW ATMOSPHERIC PRESSURE; HEATING MEANS POSITIONED WITHIN SAID CHAMBER MEANS, FOR HEATING THE PRODUCT CONTAINERS AND THE PRODUCT TO BE FREEZE DRIED; SEALING MEANS POSITIONED WITHIN SAID CHAMBER MEANS FOR VACUUM-TIGHTLY SEALING THE PRODUCT CONTAINERS; CONVEYOR MEANS POSITIONED WITHIN SAID CHAMBER FOR ENGAGING THE RIDGES OF PRODUCT CONTAINERS TO TRANSPORT THE CONTAINERS IN PROXIMITY TO SAID HEATING MEANS AND TO SAID SEALING MEANS. 